The present invention relates to a golf club putter head of a putter.
Terms and names with respect to golf club and golf play in this specification are those which are defined in official golf rules and those which are commonly accepted among golfers, and are used in the specification according to the spirit of official golf rules.
While golf clubs except putters are designed to drive and fly a golf ball for a desired distance, putters are designed to roll the ball (about 42.6 mm in outer diameter) on a putting green (where grass is cropped short for easier rolling of the ball) into or nearer a cup (about 108 mm in inner diameter) located in the green.
A putter shot, which is final in each hole (generally, a golf course has 18 holes), is said to be most mentally affected and requires very delicate controls of feeling and of force to be imparted to the ball. The slightest failure in address (posture for setting golf club beside and without contacting golf ball preparatory to hitting the same) as well as in swinging the club may greatly affect rolling of the ball hit.
FIGS. 1 to 3 are a schematic perspective view, a top view and a front view of a traditional putter with the simplest design, respectively.
The putter with the simplest design comprises a face member F, a neck N, a shaft S and a grip GR (omitted in FIGS. 1 to 3; see FIG. 17) continuous with a top of the shaft S. A part including the face member F and the neck N is called a putter head.
According to official golf rules, the neck N is not indispensable for the putter head. The putter head may comprise only the face member F.
The face member F, which has a substantially flat face 1 (requirement according to official golf rules), is joined to no members at all at its back surface 3 oppositely of the face 1 and therefore is very simple in structure. A lowermost portion of the face member F defines a sole 2 which contacts or is closest to a turf surface TF.
According to official golf rules, the face member F may have any thickness providing that its strength is within a range where no adverse effects such as a spring effect are produced upon impact (instant of the face 1 striking the ball B).
There is a sweet spot SS on the face 1 which is a vital spot in that the striking energy of the putter is most effectively transmitted to the ball B when the ball B is putted by the putter at its sweet spot SS.
Position of the sweet spot SS will be substantially dependent upon vertical and longitudinal sizes and mass distribution of the face member F.
When the ball B is putted by the putter at its point away from the sweet spot SS by a distance d, a force b is produced by the ball B to urge the face 1 to rotate about a vertical axis C which crosses the sweet spot SS. The longer the distance d of the actual putting or impact point from the sweet spot SS, the stronger the force b is which urges the face 1 to rotate. Due to energy wasted for the force b, the rolled distance of the ball B becomes shorter. However, it is extremely difficult even for a professional golfer to accurately strike the ball B by the sweet spot SS of the face 1.
FIGS. 4 to 6 are a schematic perspective view, a top view and a front view of a putter head which is prevailing, respectively.
The prevailing putter head has a flange member FL attached to a back surface 3 of a thin face member F to extend along directions of toe T and heel H of the member F. This increases the size of the sole 2 in the swinging direction and the depth of the center of gravity G in the putter head (distance of the center of gravity G from the face 1) as well as moment of inertia of the putter head, so that the sweet spot SS on the face 1 is widened into a sweet spot area SSA in the directions of toe T and heel H to increase a region of sweet spot effect.
In utilization of such sweet spot area SSA, most of the prevailing putters are such that more or less deviation of the impact point from the sweet spot SS toward toe T or heel H makes less adverse effect on the rolling distance of the ball B.
Such putter head has the flange member FL and sole 2 increased in size in the direction of swinging the putter head so that the mass is concentrated to the very portion increased in size and the center of gravity G is deeper and lower (See FIG. 6). As a result, a swinging motion is readily well-balanced and backswing and downswing become smoother. Since the center of gravity G is low, a golfer can readily drive the ball B in an upper blow direction to impart top spin to the ball B, making the ball rotate smoother.
On the other hand, the position of the sweet spot SS or sweet spot area SSA on the face 1 disadvantageously becomes too low since the flange member FL is joined to the lower portion of the face 1. That is, there arises a problem that the sweet spot or sweet spot area position becomes too low in the vertical direction while the region of sweet spot effect may be widened in the directions of toe T and heel H.
FIG. 7 is a vertical sectional view of a putter head at its sweet spot SS and illustrates the position relationship between the ball B and the sweet spot SS of the face 1 upon address.
According to official golf rules, the outer diameter D of the ball B is about 42.6 mm or more and the height h-e of the horizontal equator E of the ball B above the turf surface TF is, therefore, 42.6 mm.times.1/2=21.3 mm when the ball B remains standing still on the flat turf surface TF.
In practice, however, the ball B point-contacts the turf surface TF at BL and the whole weight of the ball B (about 46 g) is supported at the point of contact BL so that the ball B should be considered to sink below the turf surface TF. Height h-t of the turf, which varies depending upon conditions of the putting green, is generally within a range of 3 to 5 mm.
Therefore, assuming that the sunk depth of the ball B in the green is 3.5 mm on an average, the height h-e in the actual putter shot on the green is estimated to be about 18 mm (42.6 mm.times.1/2-3.5 mm). When the face 1 is held vertical to the turf surface TF and the impact is made with the sole 2 being moved in close contact with the turf surface TF, the face 1 strikes the horizontal equator E of the ball B at the height h-e or intersection of the face 1 with the horizontal plane at the height of 18 mm measured vertically from the lowermost end of the sole 2 (or ordinarily the lowermost end of the putter head).
The height h-s of the sweet spot SS of the sweet spot area type putters which are now prevailing is 10 mm or so measured from the lowermost end of the putter head so that its difference from the height h-e is 8 mm or so. In other words, in most of the conventional putters, when the ball B is putted by the putter such that the sole 2 is slided on the turf surface TF with the face 1 being perpendicular to the ball B upon impact, the face 1 contacts the ball B not at the sweet spot SS but at a point above the sweet spot SS.
FIGS. 9, 10 and 11 are front views of the putter heads and the balls to show variations in putter shot upon impact with the sweet spot SS being varied in height by vertically changing the attaching position of the flange member FL to the face member F.
In order to strike the ball B by the sweet spot SS of the face 1 of a prevailing putter head as shown in FIG. 10 in which the flange member FL is attached to a lower portion of the face member F to widen the sweet spot SS into the sweet spot area SSA in the directions of toe and heel, the impact must be made with the sole 2 being above the turf surface TF by about 8 mm or so; or a lower surface below the horizontal equator E of the ball B must be struck in an upper blow direction 10 as shown by an arrow in FIG. 10. In the latter case, the face 1 contacts the surface below the equator E of the ball B in the upward direction already upon impact so that the putter head may strike the ball B by its sweet spot SS even though the sweet spot SS is low in position.
Under such circumstances, it is not too much to say that "most of the prevailing putters are designed to strike a ball in an upper blow direction".
When the ball B is struck in the upper blow direction upon impact as shown in FIG. 10, top spin 11 is imparted to the ball B to rotate the ball B in the forward direction immediately after the impact so that advantageously the ball B rolling forward receives less resistance from the turf.
However, upon impact, if the face 1 contacts the ball B at a point too low below the horizontal equator E and/or the force imparted to the ball B is too strong, the ball B is forced to fly into the air immediately after the impact and then drops on the turf surface to receive resistance from the turf with top spin 11 being imparted to the ball B. Therefore, skills in adjusting not only a degree of upper blow but also power imparted to the ball B are so difficult to acquire that even professional golfers take a relatively long time before they successively acquire such skills.
It has been said that the most positive way or principle of imparting top spin to the ball immediately after impact is such that, as shown in FIG. 9, the face 1 of the putter is made vertical upon address, strikes the horizontal equator E of the ball B with the face 1 being maintained vertical upon impact and is swung in the upper blow direction after impact.
This putting way or principle is clear and simple with respect to required conditions of the face 1 upon address and upon impact and is less dependent upon a golfer's feeling in putt shot practices. However, most of the prevailing putters cannot strike a ball by their sweet spot SS when such putting way or principle is applied or employed.
Position of a sweet spot SS on a face of a putter head is an important factor in designing a putter so as to ensure that the putter head strikes a ball by its sweet spot using the above-mentioned putting way or principle.
As described hereinbefore with reference to FIG. 7, it is understood that the position of contact of the face 1 with the ball B is not excess of 18 mm vertically measured from the lowermost end of the sole 2 when the ball B is putted at its horizontal equator E by the face 1 with the face 1 being perpendicular to the turf surface TF and the sole 2 being closest to the turf surface TF upon impact.
To intentionally make the sole 2 closest to the turf surface TF during downswing in the putter shot which shot demands for mental and delicate adjustment of power to be imparted to the ball B is accompanied with a risk of "duff" (misplay to strike the ground or the turf before striking the ball) and therefore requires extreme putting skills.
As shown in FIG. 8, in general there will be a distance h-2 between the sole 2 and the turf surface TF (or height of the sole 2 from the turf surface TF) on the order of 3 mm on average, though this varies from one golfer to another. Therefore, when the putter strikes the ball B upon impact with its face 1 being perpendicular to the turf surface TF, the face 1 is estimated to contact the ball B at the sweet spot area SSA at a height which is within 3 mm above or below the line of intersection of the face 1 with a horizontal plane SF (to be referred to as sweet spot reference plane SF hereinafter) whose height is 15 mm measured vertically from the lowermost end of the putter head.
Such estimated position of the sweet spot area SSA (or 15 mm.+-.3 mm from the lowermost end of the putter head) is substantially consistent with results of shot tests conducted by pasting a mark sheet over the face of the putter head.
It follows therefore that when impact is made with the face 1 of the putter being perpendicular to the turf surface TF, the height of the sweet spot SS on the face 1 are to be substantially equal to the height of the intersection of the sweet spot reference plane SF with the face 1. It is therefore understood that in prevailing putters having sweet spot area SS widened in the directions of toe and heel, the position of the sweet spot SS is too low to perform the putting in the way described above.
In order to raise the position of the sweet spot SS higher than that of the sweet spot SS widened in the directions of toe and heel as in the prevailing putters, the putter head must be enlarged to increase the height of the face member; or a flange member must be joined to the back surface of the face member such that the mass distribution of the face member is concentrated to a higher position.
A putter with such an enlarged putter head once prevailed but is rarely used now since the weight of the putter head was increased accordingly to cause problems of materials to be used and of feeling.
Joining a flange member to a back surface of a face member at a higher position can raise the sweet spot SS on the face at least adjacent to a position adjacent to the joint of the flange member to the face member. Such idea of adjusting in height the position of the sweet spot SS of the putter head by selecting the joining position of the flange member to the face member is efficient in designing a putter head. However, when the position of the sweet spot SS on the face 1 is too high, the face 1 tends to be swung in a down blow direction as shown in FIG. 11 so that back spin 12 is imparted to the ball B, resulting in difficulty of controlling the distance over which the ball rolls.
As described above, in the prevailing putter heads, the effective region of the sweet spot SS on the face is widened in the directions of toe and heel for compensation of more or less deviation of the contact of the face with the ball from the sweet spot SS in the directions of toe and heel.
Since great importance in design is attached to such compensation of deviation in the directions of toe and heel, the effective region of the sweet spot SS in the vertical direction tends to be low. As described above, it is said that the putters now prevailing are designed for putting in an upper blow direction; a golfer must intentionally control the face of the putter in the upper blow direction just before the impact so as to attain contact of the face of the putter head with the ball B at its effective region of the sweet spot SS. Accuracy of the putting is greatly dependent upon feeling and skill of a golfer. It is said that in order to acquire know-how of putter techniques, professional golfers use a substantial part of practice time on the green.
As described above, with the conventional putters, even professional golfers take a considerably long time before they can acquire the skill of putting so as to make the face of the putter accurately contact at its effective region of sweet spot SS with the ball and to impart a degree of top spin depending upon a distance over which the ball is to roll, thereby controlling the rotation of the ball. In the case of a mature golfers with poor stroke skill who can afford only a short time for practice compared with professional golfers, it is next to impossible to acquire the above-described skill or technique. Every golfer realizes that when he or she fails to contact the effective region of the sweet spot SS of the face with the ball, response is not satisfactory and the ball tends to stop rolling short of the cup.
Effective in view of the above is a proposal for joining the flange member to the back surface of the face member such that the distribution of is concentrated to the joint surface of the face member with the flange member and the sweet spot area SSA is defined on the face opposite to the joint surface of the face member with the flange member.
FIG. 12 is a schematic perspective view of a putter head devised for alignment between the center of the sweet spot area SSA and the line of intersection SX of the reference plane SF with the face 1.
When the vertical center of the joint surface of the flange member FL is aligned with the sweet spot reference plane SF at the back surface 3 of the face member F, the more the flange member FL extends, the greater the difference in mass between the face and flange members F and FL becomes so that the center of the sweet spot area SSA is located closer to or is substantially aligned with the line SX of intersection between the reference plane SF and the face 1. It follows therefore that even though there may be some differences depending upon shape and mass distribution of the face member F, at least part of joint of the flange member FL must be within the range of the sweet spot reference plane SF.+-.3 mm in which the face contacts the ball B upon impact.
When the flange member FL joined to the back surface 3 of the face member F further extends as shown at FL-L in FIG. 12, the center of gravity of the putter head is caused to be located backwardly. As a result, a golfer feels to putt the ball B by the leading end of the flange member FL rather than by the face 1. In other words, the golfer feels as if he or she struck the ball by a nail-striking face of a hammer.
The above-described hammer type putter is said to be an ideal putter owing to its high probability of cup-in. However, the length of the flange member FL is limited since the official golf rules stipulate that "distance from heel to toe of a club head must be longer than distance from the face to the rear surface thereof (W&gt;L) and each club must have a shape or structure which is not essentially different from that in accordance with the tradition and customs."
Even when the length of the flange member FL of the putter of the type shown in FIG. 12 is selected within the range of W&gt;L, there may be a possibility that a golfer has a feeling of physical disorder as compared when the conventional putter is used. The feeling of physical disorder presents a serious problem since mental control of the body greatly affects the putting.
Moreover, thinness or narrowness of the sole F-2 defined at the lowermost end of the thin face member F may cause a golfer to have a feeling of instability upon address and fear of "duff" during putting.